Formulation of Steinernema yirgalemense in gel for long-term storage at room temperature

Abstract

The use of entomopathogenic nematodes (EPNs) offers the potential of reducing the use of chemical insecticides in the agricultural industry. Hydrogels for the long-term storage of EPNs may have the potential to improve the storage ability of EPNs. In this study, infective juveniles (IJ) of a South African isolate Steinernema yirgalemense were formulated in different gels, which included a laboratory grade and consumer grade of agar, as well as STOCKOSORB® 660, and compared it with IJ in water. Their survival and pathogenicity of the IJ were investigated at 25 °C. The last instar larvae of Tenebrio molitor were used to test the pathogenicity of the IJs 6 weeks postformulation. IJs stored in 1% and 1.5% agar formulations were found to provide the best survival of 77% and 82% after 6 weeks in formulation. Results indicate consumer grade agar to be comparable with laboratory grade and can be used as a cheaper alternative for the formulation of S. yirgalemense. When comparing the STOCKOSORB® 660 formulations, 80% IJ survival was recorded in a formulation of 1 g in 50 ml of water, with 50% of the IJs surviving in a formulation of 1 g in 100 ml of water. The IJs formulated and stored in STOCKOSORB® 660 gel were found to be more virulent to Tenebrio molitor than were the IJs formulated in agar.